Field of the Invention
This invention relates to a blade cleaning device for an electrophotographic image forming apparatus and more particularly to a blade cleaning device for cleaning off toners remaining on the surface of an electrophotoreceptor by applying the edge of a cleaning blade to the surface of the photoreceptor.
Generally in an electrophotographic image forming apparatus such as an electrophotographic copier, a rotatable photoreceptor having an image retaining member such as a photoconductive layer is formed in a drum shape to form a copy image from an original. In the abovementioned apparatus, an electrically charging means, an exposing means, and a developing means are arranged respectively around the circumference of the rotating photoreceptor and an electrostatic latent image is thereby formed according to an original image and the latent image is developed with developer containing toner. Thereafter, the visible image thus obtained by the development on the photoreceptor is electrostatically transferred to a transfer material such as a plain paper and the visible toner image is fixed onto the transfer material. In the meantime, the remaining toner is removed from the photoreceptor after transfer by means of a cleaning means so that the apparatus may be ready for the succeeding image formation.
Heretofore, blade cleaning apparatus has been widely used to serve as the cleaning means. In a blade cleaning method, an elastic member such as an urethane rubber plate is brought into pressure contact with a photoreceptor surface. Specifically one side of the elastic member is supported by a holding member and the edge portion on the opposite side of the elastic member is brought into pressure contact with the photoreceptor surface by utilizing elasticity of the elastic member. The photoreceptor surface and the edge portion of the elastic member are moved relatively, and thus the residues such as toner on the photoreceptor surface are cleaned off from the photoreceptor surface.
This method is characterized in that the cleaning performance is superior to the other cleaning method, the residual amount of toner can be reduced after cleaning, and the cleaning performance thereof can be maintained for a long period of time.
It is, however, not easy to bring a blade into even pressure contact with the surface of the photoreceptor and therefore partial cleaning failure occurs very frequently.
Blade cleaning apparatus having been used so far comprises a cleaning blade, a holding member or a holding frame for holding the cleaning blade and a mechanism for bringing the cleaning blade into pressure contact uniformly with a photoreceptor through the holding member. To the cleaning blade itself, a very careful attention has been paid and inter alia to the mechanical accuracy and the elasticity thereof.
With the holding member, the blade is held thereby in the direction of the thickness of the blade and the holding member is provided on the perimeter of the center portion thereof with a rotatable member such as a rotatable shaft or ratatable hole, in the longitudinal direction of the blade.
In the blade pressing mechanism, the blade is brought into pressure contact with the photoreceptor surface with a suitable pressure and with the support of the holding frame, and the edge of the blade is positioned so as to make the blade fit with the surface by making an suitable angle to the photoreceptor surface.
FIG. 1 illustrates a method for holding is conventional type of blade, which is described in Japanese Patent Publication Open to Public Inspection No. 43342/1973. FIG. 1 is a cross-sectional view showing the central portion of a drum taken from the rectangular direction to the drum shaft. Numeral 1 is a cylindrical photoreceptor drum rotatable around a rotation axis 1.sub.0. 2 is a plate-shaped elastic blade which is held by a holding frame comprising support plates 3 and 4 so that the blade and the holding frame can be united in a body. Hole 31 is provided on the perimeter of the central portion of the support plate 3 in the longitudinal direction, i.e., in the vertical direction in the drawing. The holding member is arranged to be rotatable by fitting the hole 31 to the shaft 5 of the blade pressing mechanism. As stated above, the shaft 5 has so far been positioned vertically to the plane of a blade, for the convenience of fitting. Namely, blade 4 has been designed so as to be able to rotate in parallel with the horizontal plane taken on line h--h. On the other hand, the plane taken on shaft 1.sub.0 -contact line 1.sub.a of blade 2 with photoreceptor 1 has been positioned so as to make an angle of .theta..degree. with the horizontal plane. There has been almost no study on an angle of .theta..degree. made between the rotation surface (in parallel with the plane h--h) of the blade 2 and the plane taken on the contact line 1.sub.a -the shaft 1.sub.0.